The invention relates generally to a technique for fault diagnosis in emission control systems, and more particularly to a technique for detecting faults in selective catalytic reduction units.
Industrial emissions such as nitrogen oxides and sulphur dioxide create environmental pollution. Environmental pollution is regulated in most industries. Stringent regulation requirements are being adopted by governments and standard bodies in order to minimize the discharge of noxious gases into the atmosphere by industrial facilities. Typically, an emission control system includes a reduction reactor where the industrial emanations are chemically treated with a reductant to reduce emissions. Specifically, a reductant such as ammonia is injected into the exhaust gas stream entering the reduction reactor to reduce emissions such as NOx from the exhaust gas stream.
Analysis and control of exhaust emissions is performed to comply with the regulation requirements. Emission analysis may be performed continuously by using a gas composition analyzer installed in the exhaust stack. Alternatively, the emission analysis may be performed using the gas composition analyzer connected to the exhaust stack through an extractive system. However, continuous analysis is expensive due to installation cost, maintenance and calibration requirements. A computer based model may be used to predict emissions such as nitrogen oxide (NOx) emission in order to reduce the cost of analysis of emissions. A number of predictive parameters associated with the fuel conversion process such as temperature and reductant coverage area are used by the computer based model to determine an estimate of the amount of the emissions.
Methodologies used in the past include nonlinear statistical, neural network, eigenvalue, stochastic, and other methods of processing the input parameters from available field devices and to predict process emission rates and combustion or process efficiency.
Emission control systems in power plants may experience deterioration in performance and develop faults during operation. Analysis based emission control techniques are not fully effective in the presence of faults. Knowledge of faults may be used in improvising the effectiveness of the emission control techniques. Detection of faults also helps in foreseeing failure of components and preparing for a planned maintenance schedule.